In the field of polymeric carbohydrate compounds based on natural materials, guar and its derivatives, such as hydroxyalkyl guar and/or carboxyalkyl guar, are of considerable importance for many industrial applications. The guar-based swelling agents normally used in the form of more or less fine powders are distinguished by their extremely effective thickening when dissolved in aqueous phases. There are reliable methods for controlling the viscosity of correspondingly thickened aqueous treatment solutions using both selected products based on guar or its derivatives and, in particular, suitable crosslinking agents which enable viscosity in the aqueous phase to be additionally controlled through nonionic, anionic and/or cationic mechanisms. The technical questions involved here are discussed in numerous prior art publications, cf. for example Davidson, Handbook of Water-Soluble Gums and Resins, Chapter 6, McGraw-Hill, London (1980).
It is known that the class of useful materials of natural origin in question here is characterized by carbohydrate polymer compounds which are made up at least by far predominantly of mannose and galactose units. The primary hydroxyl group in the C.sub.6 position is particularly suitable for derivatization, although secondary hydroxyl groups of the polymer skeleton may also be derivatized. The rheological and other properties of the water-based treatment liquids ultimately required can be controlled very precisely by optional purification of the natural basic material and/or by derivatization in the sense discussed above and optionally by using crosslinking agents.
So far as industrial-scale operation is concerned, difficulties can lie in the early phase of the interaction between the dry guar-based powder and the aqueous phase. An overly rapid interaction between the dry powder and the aqueous phase which is kept in particular at low temperatures results in the formation of solid particles which form gel-like lumps and of which the gel shell prevents further penetration of the aqueous phase into the interior of the lump and is thus a serious obstacle to uniform dissolution and dispersion of the solid material in the aqueous phase. Difficulties of this nature arise in particular when, on an industrial scale, considerable quantities of correspondingly thickened aqueous treatment liquids have to be produced in situ and delivered directly to the point of use. A typical example of this is the use of guar-thickened treatment solutions in the on-shore and/or off-shore development of natural useful materials, such as petroleum, natural gas, water and the like. Aqueous polymer systems are often used in the servicing of boreholes (for example cleaning, periodic stimulation and the like). Polymers capable of establishing high and predetermined viscosities are particularly useful for this purpose. Guar and guar derivatives or mixtures thereof with other auxiliaries, particularly crosslinking agents are prominent in this regard. In chapter 6-10, for example, the literature reference cited above describes the use of correspondingly thickened water-based frac fluids for restoring or increasing the production capacity of corresponding wells. The frac fluid system generally involves the use of so-called proppants (in by far the majority of cases sand), the function of the frac fluids pumped into the borehole from below being on the one hand to penetrate into the area around the well bearing useful material and, on the other hand, to introduce the entrained proppants into the new channels opened up in order further to enhance their effect.
The use of water-soluble polymer compounds in the oilfield is also described in a number of prior art publications, of which the following are cited by way of example: Society of Petroleum Engineers (SPE) of AIME-SPE 9288, 1980 "APPLICATIONS OF WATER-SOLUBLE POLYMERS IN THE OILFIELD"; SPE 25205 (1993) "Crosslinked Borate HPG Equilibria and Rheological Characterization"; SPE 26559 (1993) "Fluid Selection for Fracturing High-Permeability Formations" and SPE 25490 (1993) "An Improved Method for Measuring Fracturing Gel Break with Resin-Coated Proppant". Further particulars of the technical problems involved can be found in these literature references.
For the use of guar or guar derivatives as a thickener and viscosity generator in water-based treatment liquids for servicing boreholes, a particular form of presentation has been developed for the powders based on guar or guar derivatives which meets the various requirements of this particular application particularly well. The guar-based dry powders are mixed with substantially equal quantities of water-insoluble, liquid hydrocarbon compounds to form a high-solids, but flowable or pumpable dispersion. Hitherto, diesel oils or at least substantially dearomaticized hydrocarbon fractions of equally low viscosity have hitherto been used as the organic liquid phase. This pumpable concentrate may be continuously mixed in during introduction of the water-based treatment fluid into the borehole. The guar-based fine-particle useful materials swell after a certain time. This ensures that the fine-particle swelling solid is uniformly incorporated in the entire aqueous phase. The occurrence of undesirably rapid surface swelling and hence interference with swelling through the system are also eliminated.
The teaching according to the invention starts out from this particular preparation of guar and guar derivatives for the production of water-based treatment solutions of controllable viscosity. The problem addressed by the teaching according to the invention was to improve this principle in several respects. Liquid hydrocarbon compounds of the type hitherto used for the purpose in question are potential pollutants with only limited degradability, particularly in the off-shore sector. Quite apart from this, however, technical effects are also in need of improvement. The known highly concentrated mixtures of powder-form guar or corresponding guar derivatives and pure liquid hydrocarbon compounds under discussion here show only limited dispersion stability. After storage for several hours with no movement of the multicomponent mixture, the guar solids sink to the bottom of the storage container with simultaneous phase separation into a predominant solid phase and a supernatant liquid phase. Resulting errors in the metering of predetermined quantities of the solid phase into the water-based servicing fluid endanger the process as a whole. Accordingly, the guar dispersions used hitherto require the use of stabilizers and/or thickeners in the oleophilic liquid phase.
The teaching according to the invention as described hereinafter is based on the discovery that substantial improvements and simplifications in many respects can be achieved by replacing the at least predominant part of the organic hydrocarbon-based liquid phase with selected hydrocarbon oils derivatized with polar groups.